It was recalled that clusters of 4 atomic vacancies had been found, in Au nanoparticle-embedded MgO, by means of positron lifetime spectroscopy. These clusters were also suggested, by the results of 1-detector measurements of the Doppler broadening of annihilation radiation, to be located at the surfaces of Au nanoparticles. Evidence was provided here, using 2-detector coincidence experiments on Doppler broadening, which confirmed that these vacancy clusters resided on the surfaces of Au nanoparticles. A method was also demonstrated for the identification of defects at nanomaterial interfaces. This involved a combination of positron lifetime spectroscopy (which indicated the type of defect) and 2-detector measurements of the Doppler broadening of annihilation radiation (which revealed the chemical environment of the defects).

Positronic Probe of Vacancy Defects on Surfaces of Au Nanoparticles Embedded in MgO. J.Xu, J.Moxom, B.Somieski, C.W.White, A.P.Mills, R.Suzuki, S.Ishibashi: Physical Review B, 2001, 64[11], 113404 (4pp)